The present invention relates generally to automatic heating appliances, and more particularly to an automatic heating appliance for controlling heating by recognizing, or discriminating, the distinctive feature of an object of be heated with an ultrasonic sensor.
Known as a heating appliance in which the heating time period is automatically controlled is a microwave oven in which the cooking time period is controlled using a humidity sensor or a gas sensor for detecting vaper or various gases generated from the heated food. Further realized are heating apparatus of the types in which the temperature of the surface of a food is detected by means of an infrared sensor, i which the weight of a food is detected by a weight sensor and in which the both of the surface temperature and food weight are detected thereby. An important problem in these prior heating appliances is that the heating control can be performed under the condition that the kind, or class, of an object and the category of cooking are inputted, for example, through keys on an operating panel. That is, the finishing temperature of the object is varied in accordance with the category of cooking. Generally, there is the difference in finishing temperature between the case of reheating the food and the case of thawing a frozen food, for example, the former being about 70.degree. C. to 80.degree. C. and the latter being about 0.degree. C. to 10.degree. C. Furthermore, the heating time period to be taken is also varied in accordance with the kind of material. Since the prior sensors cannot detect the category of cooking and the kind of material, the heating appliance requires instructions in terms of the cooking category and the kind of food material for automation of the cooking. The inputting thereof is troublesome and hence a further improvement would be required from the viewpoint of simplification of handling of the apparatus.